Dual insulated magnet wire

ABSTRACT

A magnet wire having surprising characteristics comprising a base insulation of a strip of wire insulating material extending longitudinally of the conductor and being wrapped around the conductor, secured at the seam with an adhesive, and a top coat of resinous material superimposed on said base insulation. The magnet wire of this construction is able to (1) withstand temperatures for short times greatly in excess of the melting temperature of the seam adhesive without the base insulation unwrapping from the conductor, and (2) exhibit improved slip, abrasion resistance, moisture resistance, and electrical insulating characteristics.

United States Patent [191 Hilker et al.

[111 3,842,192 [451 Oct. 15, 1974 DUAL INSULATED MAGNET WIRE [75] Inventors: George D. Iiilker; Charles E. Doehrman; Verne l-I. Lausen; Harold P. Mowery; Mike T. Sutton, all of Fort Wayne, Ind.

[73] Assignee: Phelps Dodge Industries, Inc., New

York, N.Y.

221 Filed: May 17,1973

211 Appl. No.: 361,121

[52] US. Cl.. 174/120 SR, 174/121 SR, 174/121 B, 336/205 [51] Int. Cl. H0lb 7/02 [58] Field of Search 174/121 R, 1 SR, 1 B, 120 SR, 174/120 FP, 113 R; 336/205 [56] References Cited UNITED STATES PATENTS 1,944,870 1/1934 Apple 336/205 X 3,239,598 3/1966 3,412,354 11/1968 3,528,852 9/1970 11/1971 Sugiyama 174/113 R 7/1972 Trunzo 336/205 OTHER PUBLlCATlONS Dummer et. a1. Wires & R. F. Cables, Pitman, London, 1968, p. 21 & 25.

Primary Examiner-E. A. Goldberg [5 7 ABSTRACT 9 Claims, 4 Drawing Figures 1 DUAL INSULATEDMAGNET WIRE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a magnet wire, and more particularly, to a dual coated magnet wire in which the base insulation is a strip of wire insulating material extending longitudinally of the conductor and wrapped on the conductor.

2. Description of the Prior Art Magnet wires having a base insulation overcoated with a top coat of a material different from the base insulation material have long been commercially available. In fact, for many years, such magnet wire has been manufactured in a continuous process by applying several coats of base insulation material, baking each coat as it is applied, and applying a top coat or several top coats over the base insulation material, again baking each coat separately. This is normally achieved utilizing conventional wire coating machines and crossstringing the ovens. In such a process, the baking conditions of the base insulation and the top coat must be compatible or essentially the same or different baking chambers must be used.

Cables and the like have been wrapped with an elongated strip of material, usually paper and/or a metal shield, and covered by an extruded jacket of resinous material. However, this art is only remotely related to the production of magnet wire. Additionally, magnet wire has in the past been insulated by wrapping the conductor with a strip of insulating material. Both helically wound insulating and longitudinally wrapped insulation have hereintofore been disclosed.

However, heretofore, it does not appear that it has ever been suggested to improve magnet wire insulated by a wrapped base insulation by applying a top coat superimposed on said base insulation. Thus, heretofore, magnet wires insulated by wrapping strip material about the conductor have in general had the physical and electrical properties of the strip material. Overcoating the wrapped conductor has heretofore not been thought to be advantageous.

It is therefore desirable to provide a dual coated insulated magnet wire having a base insulation of an elongated strip of insulating material wrapped on the conductor, an adhesive to secure the wrapped material at the seam, and a top coat of resin material superimposed on the base insulation. Such a magnet wire has been found not only to be advantageous inasmuch as the thermal properties are better than suspected; but the magnet wire may also have improved slip and abrasion resistance, moisture resistance, and electrical insulation resistance, imparted by the resinous top coat. It is also desirable to utilize a top coat of a heat-softenable resinous material which would permit bonding adjacent turns of wire in a winding together and negate the need of an impregnating varnish.

SUMMARY OF THE INVENTION It is therefore a primary object of the invention to provide an improved magnet wire.

Another object of this invention is to provide an improved magnet wire having an insulation of an elongated strip or strips of wire insulating material extending longitudinally of the conductor and wrapped about the conductor.

Another object of this invention is to provide an improved dual coated magnet wire having a base insulation of an elongated strip of wire insulating material extending longitudinally of the conductor and wrapped about the conductor, adhesively sealed at the seam, and a top coat of resinous material superimposed on the base insulation.

Another object of this invention is to provide an improved dual coated magnet wire having a top coat of heat-softenable resinous material permitting the bonding of adjacent turns of wire in a winding and negating the need of impregnating varnishes.

A further object of this invention is to provide an improved magnet wire of the type having an insulation of an elongated strip of wire insulating material extending longitudinally of the conductor and wrapped about the conductor which has improved thermal properties, improved slip and abrasion resistance, moisture resistance, and improved electrical properties.

In the broader aspects of this invention there is provided a dual coated magnet wire having a base insulation of an elongated strip of wire insulating material extending longitudinally of the conductor and wrapped about the conductor and a top coat of resinous material superimposed on the base insulation.

The above mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary perspective view of the magnet wire of the invention;

FIG. 2 is a cross-sectional view of the magnet wire of the invention having a conductor of a circular crosssection, a base insulation of an elongated strip of wire insulating material with a width dimension slightly in excess of the circumference of the conductor;

FIG. 3 is a cross-sectional view of the magnet wire of the invention having a conductor with a circular crosssection and a base insulation of an elongated strip of wire insulating material having a width approximately twice the circumference of the conductor; and

FIG. 4 is a crosssectional view of the magnet wire of the invention having a conductor with a rectangular cross-sectional shape (although this may also be a square shape) and a base insulation of an elongated strip of wire insulating material with a width substantially equal to three times the sum of the height and width dimensions of the conductor.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, the magnet wire of the invention comprises a conductor 10 and a base insulation 12 of an elongated strip of wire insulating material, a seam adhesive 13, and a top coat 14 of a resinous material superimposed on the base insulation 12.

The conductor 10 may be either a round conductor I6 having a cross-section taken transversely thereof which is circular in shape, or a rectangular or square conductor 18 having a cross-section taken transversely thereof which is either rectangular or square in shape.

The term rectangular is use herein to include both rectangular and square shapes. Round and rectangular conductors are used commercially. Also, conductors 16 and 18 are usually either of copper or aluminum; however, nothing herein is intended to limit the disclosure to these metals.

The base insulation 12 comprises an elongated strip of wire insulating material which extends longitudinally of the conductor and is wrapped around the conductor. Each strip has a width dimension which is slightly larger than the circumferential dimension of a round conductor or the equivalent dimension of a conductor having a rectangular cross-section, such that the longitudinally extending peripheral portions thereof adjacent to the opposite edges of the strip overlap to provide a means of bonding the material to itself. Specifically, referring to FIG 2, a strip 24 is shown having a width dimension slightly in excess of the circumferential diameter of the conductor 16 wrapped around the conductor so as to have peripheral portion 26 adjacent to edge overlaying the peripheral portion 28 adjacent to edge 22. These elongated lapped portions 26, 28, extend longitudinally of the conductor, and the seam adhesive 13 is positioned therebetween. Both the lapped portions 26, 28 and the adhesive 13 extend the entire length of the insulation.

Referring to FIG. 3, there is shown, in similar fashion, a strip 30 having a width approximately twice the circumference of the conductor 16. Strip 30 also has longitudinally extending peripheral edges 20, 22 and lapped portions 26, 28. The entire conductor is covered with at least two layers of strip 30 in contrast to the single layer of strip 24, as previously described.

Similarly, FIG. 4 illustrates a conductor having a rectangular cross-section in which the base insulation comprises a strip 32 having a width dimension which is about one and one-half times the distance around the conductor, or about three times the sum of the width and the height of the conductor 18. Again, strip 32 has longitudinally extending edges 20 and 22 and overlapping portions 26, 28. A feature of the rectangular conductor shown in FIG. 4 not possessed by the circular conductor shown in FIGS. 2 and 3 is the fact that the overlapping portions 26 and 28 overlap over one width and one length dimension of the conductor 18. Thus, the base insulation 12 of the magnet wire illustrated in FIG. 4 comprises a single thickness of strip 32 on two sides of the conductor and a double thickness of strip 32 on the remaining two sides of the conductor. Such a design has usefulness in the construction of windings inasmuch as the insulation between turns is always at least three layers of strip 32 while a minimum of insulating material is consumed. This construction, however, shall not be a limitation as other lap configurations are possible and in some applications, desirable.

Still referring to the drawings, mention must now be made of the resin top coat 14. In all of the magnet wires illustrated in the drawings, top coat 14 is superimposed over the base insulation 12 and completely surrounds the base insulation and is coincident therewith. It can be seen by the drawings, that none of the adhesive 13 is positioned between the base insulation and the conductor. Such is preferred inasmuch as either may cause bonding of the base insulation to the conductor and result in a magnet wire insulation which cannot be easily stripped, when desired.

The wire insulating material of the base insulation 12, 24, 30 and 32 can be chosen from a wide variety of materials. Heretofore, magnet wires having insulation of wrapped strip material has generally been limited to those materials which cannot be applied by the more usual method, i.e., from solution, using conventional wire coating machines. These materials have included various types of paper, polyimides such as Nomex" strip material as sold by the Dupont Company, and Kapton strip material as sold by Dupont Company. Other materials which can be applied as strip material in accordance with the invention include asbestos, woven fabrics, such as of glass fiber, and non-woven strands of fiberous materials. The use of many of these sheet materials for wire insulation has been limited heretofore inasmuch as it was thought that the thermal properties of such magnet wire could be no better than the thermal properties of the adhesive with which the insulation was secured to the conductor. Thus, sheet wire insulating material having extremely good electrical properties were not used if the adhesives necessary to adhere the same to wires had poor thermal properties. However, a magnet wire made in accordance with the invention does not have this limitation and thus these wire insulating materials have now become useful. The seam adhesive 13 can be any of a large family of commercially available as well as proprietary bonding agents.

The resinous material of the top coat 14 can be any number of resinous materials. Any of the available resinous materials including polyesters, polyamides, including NYLON polyamides, polyimides, polyamide imides, epoxys, phenoxys, polyvinyl formal, polyvinyl butyrals, polycarbonates, polypropylene, and the like can be used. The use of each of these resinous materials will impart to the magnet wire the slip and abrasion resistance associated with a wire coated with that resinous material. By choosing a resinous material having better slip and abrasion resistance than the insulating material of the base insulation, these properties of the magnet wire can be enhanced over prior art magnet wires having wrapped insulations. By the use of a top coat 14 of resinous material over porous base insulation materials, the moisture resistance and the electrical insulating characteristics of the base insulation 12 are both enhanced. Additionally, if the resinous material of the top coat is a resinous material of the group which can be softened by heating the material above a softening temperature such as thermoplastic materials and certain polyimides and resinous materials which can be softened at elevated temperatures but technically are not thermoplastic resins, completely surprising results occur. It has been found that with the magnet wire of the invention, when the resinous material of the top coat 14 is a heat-softenable material, the magnet wire can withstand temperature excursions to well above the softening temperature of the resinous material without the base insulation becoming unwrapped or otherwise failing.

In a specific embodiment, in which the magnet wire of the invention as illustrated in FIG. 2 was fabricated by longitudinally wrapping a conductor with a strip of paper such as 32-H-C or 32-H-CC Insulflex" crepe paper as sold by Dennison Paper Company or Copaco" paper as sold by Cottrell Paper Company, Inc. and overcoating the same with a thermoplastic polyester having a softening temperature from about 425F to 475F, that magnet wire can withstand temperatures from about 600F to about 700F under which conditions the paper actually chars without the paper unwrapping from the conductor. A similar phenomenon is experienced when other resins are used as the resinous material of the top coat l4 and other insulating materials are used as the base insulation 12 in accordance with the invention.

While there have been described above the principles of this invention in connection with specific chemistry, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of the invention.

What is claimed is:

l. A dual coated magnet wire having surprising thermal characteristics, improved abrasion resistance and slip properties, improved moisture resistance, and improved electrical insulating value comprising an elongated magnet wire conductor, an elongated strip of insulating material, said strip extending longitudinally of said conductor and being tightly wrapped around said conductor to overlap longitudinally extending portions of said strip adjacent the opposite peripheral edges thereof and to exclude air therefrom thereby forming a base insulation, an adhesive only between said overlapped portions, and a layer of resinous material superimposed on said base insulation forming an overcoat thereon, said insulated conductor being able to withstand temperatures in windings for short times greatly in excess of the temperature at which said resin material loses its strength without said strip unwrapping.

2. The magnet wire of claim 1 wherein said peripheral portions of said strip overlap to an extent that the exterior of said conductor is covered by two thicknesses of said strip.

3. The magnet wire of claim 1 wherein said wire insulating material is sheet material having the desired insulating characteristics chosen from the group consisting of rope, kraft, or rag papers; polyimide, polyamide, and polyester film materials, asbestos sheet materials; fiberglass and combinations of glass and mica and asbestos cloth and mat materials.

4. The magnet wire of claim 1 wherein said resin is chosen from the group of polyester, polyimide, polyamide imides, epoxy, phenoxy, polypropylene, polycarbonates, and other film-forming resinous materials.

5. The magnet wire of claim 2 wherein said wire insulating material is a paper material which chars at temperatures from about 600F to about 700F, said resin has a melting temperature from about 425F to about 536F, said base insulation withstanding charring temperatures without unwrapping from said conductor.

6. The magnet wire of claim 2 wherein said conductor is circular in cross-section, and said strip has a width which is at least twice the circumference of said conductor.

7. The magnet wire of claim 1 wherein said conductor has a cross-section which is a parallelogram, and said strip has a width sufficiently long to at least lap itself on one side of said conductor.

8. The magnet wire of claim 1 wherein said resinous material is a heat-softenable resinous material.

9. The magnet wire of claim 5 wherein said wire insulating material is a creped paper material. 

1. A DUAL COATED MAGNET WIRE HAVING SURPRISING THERMAL CHARACTERISTICS, IMPROVED ABRASION RESISTANCE AND SLIP PROPERTIES, IMPROVED MOISTURE RESISTANCE, AND IMPROVED ELECTRICAL INSULATING VALUE COMPRISING AN ELONGATED MAGNET WIRE CONDUCT OR, AN ELONGATED STRIP OF INSULATING MATERIAL, SAID STRIP EXTENDING LONGITUDINALLY OF SAID CONDUCTOR AND BEING TIGHTLY WRAPPED AROUND SAID CONDUCTOR TO OVERLAP LONGITUDINALLY EXTENDING PORTIONS OF SAID STRIP ADJACENT THE OPPOSITE PERIPHERAL EDGES THEREOF AND TO EXCLUDE AIR THEREFROM THEREBY FORMING A BASE INSULATION, AN ADHESIVE ONLY BETWEEN SAID OVERLAPPED PORTIONS AND A LAYER OF RESINOUS MATERIAL SUPERIMPOSED ON SAID BASE INSULATION FORMING AN OVERCOAT THEREON, SAID INSULATED CONDUCTOR BEING ABLE TO WITHSATND TEMPERATURES IN WINDINGS FOR SHORT TIMES GREATLY IN EXCESS OF THE TEMPERATURE AT WHICH SAID RESIN MATERIAL LOSES ITS STRENGTH WITHOUT SAID STRIP UNWRAPPING.
 2. The magnet wire of claim 1 wherein said peripheral portions of said strip overlap to an extent that the exterior of said conductor is covered by two thicknesses of said strip.
 3. The magnet wire of claim 1 wherein said wire insulating material is sheet material having the desired insulating characteristics chosen from the group consisting of rope, kraft, or rag papers; polyimide, polyamide, and polyester film materials, asbestos sheet materials; fiberglass and combinations of glass and mica and asbestos cloth and mat materials.
 4. The magnet wire of claim 1 wherein said resin is chosen from the group of polyester, polyimide, polyamide imides, epoxy, phenoxy, polypropylene, polycarbonates, and other film-forming resinous materials.
 5. The magnet wire of claim 2 wherein said wire insulating material is a paper material which chars at temperatures from about 600*F to about 700*F, said resin has a melting temperature from about 425*F to about 536*F, said base insulation withstanding charring temperatures without unwrapping from said conductor.
 6. The magnet wire of claim 2 wherein said conductor is circular in cross-section, and said strip has a width which is at least twice the circumference of said conductor.
 7. The magnet wire of claim 1 wherein said conductor has a cross-section which is a parallelogram, and said strip has a width sufficiently long to at least lap itself on one side of said conductor.
 8. The magnet wire of claim 1 wherein said resinous material is a heat-softenable resinous material.
 9. The magnet wire of claim 5 wherein said wire insulating material is a creped paper material. 